I'm a 19-year-old Argentinian Biology student, and I've been writing fanfic for around a year.
Back then when I started writing, I hadn't even noticed there was so much discussion of OCs. I had read a few fics with them, and it seemed natural to me that there should be other characters apart from those from canon to fill certain roles.
That's how I came to write my first OCs, too; as friends or family of canon characters. They usually had minor roles. But guess what? They're taking over!
In the fic I'm writing now, Changing the Rules, there are a couple of minor OCs, a few minor characters, and two major OCs. One of them is Fionna Flannery, an OFC I was rather worried about in the beginning but that now I think is going quite well; and then there's Remus's father, Edward Lupin.
He's an interesting case. When I first planned the fic, his only role was to brew Wolfsbane. Now, not only he's one of the main characters, but he's gotten himself into much more trouble than I expected. I really enjoy writing him, though, and see how he develops. I've learnt a lot about his story by now.
And I must admit, I do think I have a crush on him...